Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997adil...mm...01m&link_type=abstract
NCSA Astronomy Digital Image Library
Astronomy and Astrophysics
Astronomy
Scientific paper
We present narrow band images at selected wavelengths in the 8-13 micron window of four carbon rich, proto-planetary nebulae that have an unusual 21-micron dust feature: IRAS 04296+3429 IRAS 22272+5435, IRAS 07134+1005 and IRAS 19500-1709. We observe axially symmetric dust emission structures in IRAS 22272+5435, and IRAS 07134+1005, tentatively in IRAS 19500-1709 while IRAS 04296+3429 is unresolved with our 1'' angular resolution. The well resolved morphology of IRAS 07134+1005 shows an elliptical outer shell surrounding two aligned peaks that we interpret as limb brightened peaks of an optically thin, elliptical shell with an equatorial density enhancement. This mid-IR morphology contrasts with that observed in the better studied carbon rich proto-planetary nebulae, AFGL 2688, AFGL915 and AFGL 618, which show bright, unresolved cores, probably created by optically thick inner regions, and bipolar extensions that align with their optical reflection nebulosities. Using an axially symmetric dust code and assuming that the dust is composed of 0.01 micron amorphous carbon grains, we model the dust emission images and the spectral energy distributions of these four proto-planetary nebulae and of the young, carbon rich planetary nebula, IRAS 21282+5050, hat also has an axially symmetric dust shell and has other similarities with the proto-planetary nebulae that have the 21 micron dust feature. Marginally resolved mid-infrared images constrain the dust shell's inner radius while well resolved mid-infrared images additionally constrain other geometric parameters of the model (e.g., inclination angles and pole to equator mass loss rate ratios). The modelling reveals that the observed axial symmetry in the dust shells of these objects coincides with an enhanced mass loss phase (3x10^(-5) M_sun/yr) during which the equatorial mass loss rate was a factor of 18 to 90 higher than the polar mass loss rate; i.e. an axially symmetric superwind. Our dynamical age estimates indicate that these stars left the asymptotic giant branch approximately 300-1400 years ago, just after the superwind phase. For each object, the size and structure of the dustshell is the same for the sampled wavelengths with the exception of IRAS 22272+5435 for which the 11.8 micron emission is larger than either the 8.2 or 9.7 micron emission. IRAS 22272+5435's spectrum has a larger dust feature to dust continuum ratio than found in the other objects and hence its 11.8 micron image is probably dominated by the 11.8 micron feature emission that has different optical properties than the underlying continuum. Editor's note: According to Meixner, the proper BUNIT for the data images Jy/pixel; for model images, flux/pixel where 1 flux = 1.16x10^(11) Jy.
Arens John F.
Graham James R.
Jernigan Garret J.
Keto Eric
Meixner Matthew
No associations
LandOfFree
Mid-infrared Images of Post-AGB Circumstellar Dustshells does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Mid-infrared Images of Post-AGB Circumstellar Dustshells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mid-infrared Images of Post-AGB Circumstellar Dustshells will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1223219